Optrode for sensing hydrocarbons

ABSTRACT

A two-phase system employing the Fujiwara reaction is provided for the fluorometric detection of halogenated hydrocarbons. A fiber optic is utilized to illuminate a column of pyridine trapped in a capillary tube coaxially attached at one end to the illuminating end of the fiber optic. A strongly alkaline condition necessary for the reaction is maintained by providing a reservoir of alkali in contact with the column of pyridine, the surface of contact being adjacent to the illuminating end of the fiber optic. A semipermeable membrane caps the other end of the capillary tube, the membrane being preferentially permeable to the halogenated hydrocarbon and but preferentially impermeable to water and pyridine. As the halogenated hydrocarbon diffuses through the membrane and into the column of pyridine, fluorescent reaction products are formed. Light propagated by the fiber optic from a light source, excites the fluorescent products. Light from the fluorescence emission is also collected by the same fiber optic and transmitted to a detector. The intensity of the fluorescence gives a measure of the concentration of the halogenated hydrocarbons.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the University of California and theUnited States Department of Energy.

BACKGROUND OF THE INVENTION

The subject invention relates generally to optical fiber spectrometryand more specifically to the fluorometric detection of polyhalogenatedhydrocarbons.

The detection and measurement of bound halogens and halogen relatedcompounds in human and animal tissues and in industrial effluents is ofvital importance for health and environmental purposes. Many commonhousehold and industrial chemicals in every day use, such as drycleaning agents, refrigerants like freon, fire extinguishers, paintremovers, fumigants, polymeric compounds, anesthetics such as halothane,enfluorane, metoxofluorane and isofluorane, and some antihelmintics,certain pesticides and fungicides contain toxic, halogenated organiccompounds which are either ingested or discharged into the environment,making these chemicals a potential, and in most instances, a real healthand environmental hazard. It has thus become important to be able todetect and even quantitatively measure or monitor the presence of thesecompounds or their metabolic products, so that the levels of theiringestion or discharge into the environment may be controlled.

As a consequence, several methods and instruments have been devised tomeasure these halogen containing organic compounds. Some of thesemethods for detecting gaseous halohydrocarbons use electron capture orpiezo electric devices. Some other methods have been devised to detectorganic halocomponds, especially in the liquid or aqueous phase. Onesuch method is based on the reaction of halogenated hydrocarbons withpyridine or pyridine derivatives in an alkaline medium to yield highlycolored products. It is known in the art that when a gem-polyhalogencompound, which is a compound that carries more than two halogen atom onthe same carbon, is heated with pyridine in a strongly alkaline medium(pH 10-11), such as in the presence of sodium or potassium hydroxide, anintensely red product, exhibiting absorption maxima at about 368 mu andat about 535 mu, is formed. This reaction scheme, shown in equation 1below, ##STR1## is known as the Fujiwara reaction (K. Fujiwara, Sitzfer,Abhandl. Naturforsch. Ges. Rostock., 6, 33, (1941); G. A. Lugg, Anal.Chem., 38, 1532 (1966); T. Uno et al., Chem. Pharm. Bull., 30, 1876(1982)). The Fujiwara reaction has become a classic method for thedetection of halogenated hydrocarbons in a given sample or analyte inthe liquid phase. However, for a quantitative measure of halogenatedhydrocarbons in an analytical or test solution or sample, the Fujiwarareaction presents some problems, due to the insolubility of pyridine inreagents normally used to generate the necessary alkalinity and thedifficulty in being able to control the rate of diffusion of the OH⁻ ionfrom the aqueous phase into the organic pyridine phase.

More often, the reaction consists of a two-phase procedure whereby thegem-polyhalogen compound, pyridine and aqueous sodium or potassiumhydroxide are combined, mixed, and heated for a predetermined length oftime until an intensely red color develops. The pyridine phase is thenseparated from the alkaline phase by conventional methods. Absorptionspectra of the colored product are measured thereafter. The amount ofthe chromophoric product formed is dependent on the amount and rate ofdiffusion of the hydroxide ion into the pyridine phase of the mixture.Since this diffusion is difficult to control, reproducibility ofmeasurements becomes extremely difficult and unpredictable.

A one phase procedure using pyridine-water-sodium hydroxide has alsobeen employed to avoid the pitfalls of the two phase method (G. A. Lugg,supra). There have also been several modifications of the Fujiwarareaction, such as different solvents, different bases, varyingtemperatures, varying concentrations of sodium hydroxide, time ofreaction and the like, to minimize the difficulties encountered and tomake the reaction more widely accessible.

U.S. Pat. No. 3,472,626 issued to Law, discloses a method for thedetection of organic halogen containing compounds in aqueous liquids, bythe use of the salt of a pyridine base and either caustic soda orcaustic potash.

Still other problems are encountered in the measurement of thesehalogenated hydrocarbons or their metabolic products in environmentaland tissue samples. These compounds are found at extremely low levels intissues, groundwater samples or effluents, which tend to make thereproducibility and reliability of any measurements difficult. It wouldalso be desirable some times to be able to analyze these samples at adischarge site which is remote from the site of the detection equipmentand continually monitor the levels of these compounds in various samplesfrom a remote monitoring site.

Laser based remote fiber spectroscopy offers a wide range ofpossibilities for the in situ detection and quantification of not onlyhalohydrocarbons but also other groundwater contaminants. Thedevelopment of high transmission, long range fiber optics and theadvantages of their use in data transmission have made fiber opticalmethods of data transmission and detection extremely attractive. The useof such fiber optics also makes it possible to trasmit or receive datasignals over distances of two or three kilometers.

It would, therefore, be desirable to have a fiber optic sensor anddetection system, for the measurement of organic halohydrocarbons intissue and environmental samples, which would not only be sensitive tomeasure low levels of these compounds but which would also be amenableto operation from a remote location.

Accordingly, it is an object of the subject invention to provide amethod for the measurement of organic halohydrocarbons in environmentaland tissue samples.

Another object is to provide a method whereby the levels of organichalohydrocarbons in tissue, ground water and other environmental samplescan be continually monitored.

Yet another object is to provide an apparatus and method which enablethe simultaneous monitoring of organic halohydrocarbons in multiplesamples of groundwater and other environmental material and tissuesamples, from a remote location.

Still another object is to provide a sensor and detection system whichcan detect not only low levels of organic halohydrocarbons but can alsobe operated from a remote location.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects and in accordance with thepurpose of the present invention as embodied and broadly describedherein, the subject invention is directed to an "optrode" and a methodfor the detection of halohydrocarbons, particularly organic chlorides,in an analyte which may be tissue, groundwater, or other environmentalsamples. As used herein, an optrode is a chemical sensor device locatedat the interface between an optical fiber and the halohydrocarbon ofinterest (the analyte) contained in a sample solution. The basic designof the optrode, according to one aspect of the subject invention,includes an optical fiber terminus comprising a porous substrate such aspolyvinyl alcohol (PVA) or control pore glass (CPG). Appropriatehygroscopic additives may be included in the PVA or CPG to maintain thenecessary water content. The PVA or CPG can be charged with specificchemical reagents which when exposed to target molecules, form achemically or physically detectable product such as for example, eithera fluorescent or fluorescence-quenching product.

In one embodiment of the instant optrode, a two-phase reagent system isplaced in a capillary tube and an optical fiber is placed inside thecapillary tube such that one end of it is either adjacent to theinterface of the two-phase reagent system or extends into the two-phasereagent system and the other end is connected to an appropriateillumination source and a detector system. For the detection ofhalohydrocarbons, an exemplary two-phase reagent system may comprisepyridine or a pyridine derivative and an alkaline reagent such aspotassium or sodium hydroxide, the two reagents being layered over eachother such that there is a surface of contact between the two. The fiberoptic illuminates the column of the pyridine or pyridine derivativetrapped in the capillary tube, which is coaxially attached at one end tothe illuminating end of the fiber optic. A strongly alkaline conditionnecessary for the reaction is maintained by the reservoir of alkali incontact with the column of pyridine, the surface of contact beingadjacent to the illuminating end of the fiber optic. Optionally, asemipermeable membrane caps the other end of the capillary tube, themembrane being preferentially permeable to the halogenated hydrocarbonand but preferentially impermeable to water and pyridine. Alternatively,an air bubble may be interposed between the test solution and thepyridine phase. As the halogenated hydrocarbon diffuses through themembrane and into the column of pyridine, fluorescent products areformed from the reaction of the halohydrocarbon with the pyridine in thepresence of the OH⁻ ions. The optical fiber transmits light from theilluminating source such as a suitable laser source, to the interface ofthe two-phase reagent system where the analyte in the test solutionreacts with the pyridine. It also transmits the fluorescent light backto the detection system. Suitable laser sources include argon laser,carbon dioxide laser, ruby laser, copper vapor laser and the like.

One embodiment of the subject method utilizes laser based remote fiberspectrometry for the detection and measurement of trace to macroconcentrations of halogenated hydrocarbons from single or multiplesamples, from the same location or multiple locations, at a site remotefrom the detection system. A laser light of the appropriate wavelengthis focused into single strand optical fibers or cables. The opticalfibers are coupled to the samples of the analyte at various locations orfrom the same locus through the optrodes. The light, after interactionwith the analyte, is collected and transmitted back through the sameoptical fibers or cables to a specially designed detection system suchas a spectrometer where the returning light is spectrally sorted andanalyzed.

Another aspect of the subject invention is a method for the detection oflow levels of polyhalogenated hydrocarbons comprising a modifiedFujiwara reaction (equation 1). The method, broadly, comprisescontaining pyridine or pyridine derivatives in a suitable container andlayered over an alkaline medium such as potassium or sodium hydroxide,such that there is a surface of contact between the pyridine and alkalilayers. When exposed to a solution of the halohydrocarbon, or to asolution suspected of containing the analyte, the pyridine reacts withthe halohydrocarbon in the presence of the alkali to yield a bright redto a reddish brown, fluorescent product. This fluorescent product isilluminated at an appropriate wavelength and the fluorescence emissionof the product is measured as a function of time or the concentration ofthe halohydrocarbon. The optrode is positioned adjacent the surface ofcontact, and in conjunction with a detection system such as afluorimeter or spectrometer. The amount and rate of formation of theproduct formed may be measured continually or at predetermined timeintervals. The detection system may also be located at a site remotefrom the site of measurement.

A preferred embodiment of the optrode or the sensor system of thesubject invention comprises a capillary tube or cuvette, 0.1 mm to 2 mmin internal diameter, preferably capped at one end. Capping, however, isnot critical for the operation of the optrode. The capping material iseither porous or semipermable, preferably semipermeable. The mostpreferred capping material is a water impermeable membrane which is alsoimpermeable to pyridine, but permeable to halohydrocarbons. Exemplarymembrane materials include but are not limited to parafilm (thinparaffin films), mylar, electrostatically treated mylar, zeflour,polycarbonate films and the like and exemplary halohydrocarbonsdetectable by the method include but are not limited togem-halohydrocarbons such as chloroform, methylchloroform,sym-tetrachloroform, phenylchloroform, carbon tetrachloride,dichloromethane, trichloroethylene, 1,1,2-trichloroethane and the like.

The instant method and optrode are suitable for monitoring volatileorganic chloride contaminants in aqueous systems. The subject optrode isable to detect and quantify sub-part-per-million to macro concentrationsof organic chlorides in aqueous solutions. The fiber optic system usedin the subject invention enables the measurement of organic chloridewhere the sample and detection system are separated by a distance ofgreater than 500 meters of optical fiber. It is also possible by the useof the subject method to simultaneously measure organic chloride contentin multiple samples from the same location or from different locationsthat are separated by several hundred meters. The subject method isspecific to organic compounds containing two or more chlorines andsensitive to approximately 0.1 part per million, and reproducible withinabout ±3%.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate one embodiment of the invention and,together with the description, serve to explain the principles of theinvention. In the drawing:

FIG. 1 gives a cross-sectional view of the optrode shown immersed in atest solution.

FIG. 2 shows the detailed construction of the optrode, according to onepreferred embodiment of the subject invention.

FIG. 3 shows absorption spectra obtained for samples of nicotinamide towhich varying amounts of chloroform were added.

FIG. 4 shows spectra of nicotinamide fluorescence with 5 ppm of CHCl₃present.

FIG. 5 shows absorption spectra at 530 nm of pyridine containing varyingamounts of CHCl₃.

DETAILED DESCRIPTION OF THE INVENTION

The subject invention is broadly directed to an apparatus and method forthe detection and measuring continually or at predetermined intervals,of organic halohydrocarbons. The key component of the apparatus istermed the "optrode" which is a special termination at the distal end ofan optical fiber, which aids in the increase, decrease or initiation ofa measurable reaction or signal when an illuminating beam of lightinteracts with the species to be measured. The illuminating light may bein the UV, visible or infrared regions. Suitable illuminating sourcesmay be any conventional sources and include but are not limited tolasers, such as argon, CO₂, ruby, copper vapor and the like. Argon laseris most conveniently used. As used herein, an optrode is, morespecifically, a chemical sensor device used at the interface between anoptical fiber and a sample solution containing the halohydrocarbon ofinterest (the analyte). The basic design of the optrode, according toone aspect of the subject invention, is the terminus of a plain opticalfiber. According to another aspect of the instant invention, the optrodeincludes an optical fiber terminus optionally comprising a poroussubstrate such as polyvinyl alcohol (PVA) or control pore glass (CPG).When PVA or CPG termini are used, appropriate hygroscopic additives maybe included in the PVA or CPG to maintain the necessary water content.The PVA or CPG can be charged with specific chemical reagents which whenexposed to target molecules, form a chemically or physically detectableproduct such as for example, either a fluorescent orfluorescence-quenching product.

The general principles of the operation of optrodes and the design andconstruction of some optrodes are described in pending patentapplication U.S. Ser. No. 06/445,619 filed Nov. 30, 1982 which is acontinuation-in-part of U.S. Ser. No. 194,684 filed Oct. 6, 1980, bothof which are incorporated herein by reference and made a part hereof.

Although many types of optrodes have been described, monitoringoptrodes, such as the optrode of the instant invention, however, have tomeet stringent requirements and applications. These optrodes, can beeither physical or chemical in nature. Physical optrodes are mechanicaland direct measuring whereas chemical optrodes, generally, utilizereagents and membranes. These reagents may be immobilized on suitablematrices or substrates or contained in appropriate reservoirs. Chemicaloptrodes can be used to measure both physical and chemical properties.Measurement of fluorescence, absorption and reflection are all suitableparameters for optrode applications. Fluorescence is most often chosenbecause of its high sensitivity, reasonable specificity and the varietyof indicators that are available. In some instances, a fluorescent tagmay be attached to a suitable reagent, thereby expanding theavailability of appropriate sensing systems.

However, several factors need to be taken into consideration in thedesign and construction of a chemical optrode. Such factors include butare not limited to (1) the selection of an appropriate chemical reactionwhich can be monitoring by means of some measurable parameter, (2) thefeasibility of fixing the necessary reagents on the fiber, (3) possibleinterference or poisoning of the optrode by extraneous components of thesample matrix, and (4) the active and shelf life of the particularoptrode.

There are three basic types of chemical optrodes. In two of these, thereagent is immobilized. In one, the reagent is trapped in a polymermatrix and in the second, it is attached to glass beads or glass rods bycovalent bonds and then glued or welded to optical fibers. The thirdtype of optrode is the reservoir type where the reagent is contained ina reservoir which is separated by a suitable membrane from the sample oranalyte. The reaction takes place on the surface of the membrane and themeasurable signal, such as fluorescence, is emitted from the surface ofthe membrane. This type of optrode is particualrly suitable when anon-reversible chemical reaction is involved and a continuous source orreplenishment of the reagent is required.

The "optrode" of the subject invention is of the third type and is achemical sensor device used at the interface between an optical fioerand a sample solution of an analyte. The basic design of the optrode ofthe subject invention, according to one aspect of the subject invention,is the terminus of a plain optical fiber. According to another aspect ofthe instant invention, the optrode includes an optical fiber terminusoptionally comprising a porous substrate such as polyvinyl alcohol (PVA)or control pore glass (CPG). When PVA or CPG termini are used,appropriate hygroscopic additives may be included in the PVA or CPG tomaintain the necessary water content. The PVA or CPG can be charged withspecific chemical reagents which when exposed to target molecules, formeither a fluorescent or fluorescence-quenching product. Appropriatehygroscopic additives maintain the necessary water content in the PVA orCPG.

In the subject optrode, a two-phase reagent system is placed in acapillary tube and the optical fiber is placed inside the capillary tubesuch that one end of it is adjacent the interface of the two-phasereagent system and the other end is connected to an appropriateillumination source and a detector system. For the detection ofhalohydrocarbons, an exemplary two-phase reagent system employed maycomprise a pyridine derivative and an alkaline reagent such as potassiumor sodium hydroxide, the two reagents being layered over each other suchtnat there is a surface of contact between the two. As used herein, theterm pyridine derivative includes without limitation, pyridine, saltsthereof, substituted pyridine, and related compounds. The fiber opticilluminates the column of the pyridine or pyridine derivative trapped inthe capillary tube which is coaxially attached at one end to theilluminating end of the fiber optic. A strongly alkaline conditionnecessary for the reaction is maintained by the reservoir of alkali incontact with the column of pyridine, the surface of contact beingadjacent to the illuminating end of the fiber optic. Optionally, asemipermeable membrane caps the other end of the capillary tube, themembrane being preferentially permeable to the halogenated hydrocarbonand but preferentially impermeable to water and pyridine. Alternatively,an air bubble may be interposed between the test solution and thepyridine phase. As the halogenated hydrocarbon diffuses through themembrane and into the column of pyridine, fluorescent reaction productsare formed. One end of the optrode is connected to the detector and theother end interacts with the test solution. The optical fiber transmitslight from the illuminating source such as a suitable laser source, tothe interface of the two phase reagent system where the analyte in thetest solution reacts with the pyridine. It also transmits thefluorescent light back to the detection system. Suitable laser sourcesinclude argon laser, carbon dioxide laser, ruby laser, copper vaporlaser and the like. Necessary illumination, coupling and detectionsystems and equipment for use with the subject optode and method aredescribed in U.S. Ser. No. 445,619 which is incorporated herein byreference. The subject optrode is employed for the quantitativedetection and monitoring of the levels of halohydrocarbons ingroundwater, environmental and tissue samples.

The optrode comprises a tube, preferably a capillary tube, 0.1 mm to 2mm in internal diameter, preferably capped at one end, although cappingis not critical for the operation of the optrode. The capping materialis either porous or semipermable, preferably semipermeable. The mostpreferred capping material is a water impermeable membrane which is alsoimpermeable to the reagents being used, but permeable tohalohydrocarbons. Exemplary membrane materials include but are notlimited to parafilm (thin paraffin films), mylar, electrostaticallytreated mylar, zeflour, polycarbonate films and the like. The membraneserves not only to preserve the integrity of the reagents but alsoprovides the required specificity to the analyses as differentorganochlorides exhibit different rates of permeability.

In an alternative embodiment of the instant optrode, a small cuvettewith two compartments may be employed. The cuvette may be of similardimensions as the capillary tube or slightly larger. The first andsecond reagents are contained in each of the two compartments. Thecompartmentalized cuvette is provided with a window between thecompartments so as to provide a surface of contact between the first andsecond reagents. A fiber optic is attached at a first or distal endthereof to the window of the container and adjacent the surface ofcontact, a second or proximate end of the fiber optic being connected toan illumination source and a detector means.

The method of the present invention comprises the two phase version ofthe Fujiwara reaction. Although under normal laboratory conditions andconventional methods of detection, both the one phase and two phaseapproaches work equally well for the detection of gem-halogen organocompounds, with the optrode sensor, the two phase method has certainadvantages. The detection of the halohydrocarbons is not affected by thefact that pyridine and, water which is needed for the reaction and as asolvent for the potassium or sodium hydroxide, are immiscible. Theconstruction of the optrode provides for the continual replenishment ofthe reactants. The general reaction scheme of the subject method isshown in equation 2 below: ##STR2## The pyridine derivative and alkaliare layered and contained in a suitable container means such that thereis a surface of contact between the two reagents. As used herein, theterm pyridine derivative includes pyridine, whether specified separatelyor not. When exposed to a solution of the analyte which is ahalohydrocarbon, or to a solution suspected of containing the analyte,the pyridine derivative reacts with the halohydrocarbon in the testsolution in the presence of the alkali to yield a detectable, redfluorescent product. As used herein, the term pyridine derivativeincludes without limitation, pyridine, salts thereof, substitutedpyridine, and related compounds. The amount or the rate of production ofthe detectable product is measured by the optrode which is positionedadjacent to the surface of contact, and in conjunction with a detectionsystem such as a fluorimeter or spectrometer. The amount of the productformed may be measured continually or at predetermined time intervals.

According to one preferred embodiment of the subject method, the alkaliis sodium hydroxide, potassium hydroxide, lithium hydroxide and thelike, sodium and potassium hydroxide being preferable. The secondreagent is a pyridine or pyridine derivative, exemplary compoundsincluding but not limited to pyridine or pyridinium salts, pyridinecarboxaldehyde, pyrazine, pyridine dicarboxylic acids, dimethylpyridine, methyl pyridine, nicotinamide, isonicotinamide,nicotine-diamide, and the like. Pyridine and nicotinamide are thepreferred reagents. Organic halohydrocarbons detectible by the subjectmethod using the instant optrode include but are not limited togem-halohydrocarbons such as chloroform, methylchloroform,sym-tetrachloroform, phenylchloroform, carbon tetrachloride,dichloromethane, trichloroethylene, 1,1,2-trichloroethane and the like.When the pyridine or pyridine-like compound comes into contact with thehalohydrocarbon in an alkaline medium, a bright colored or fluorescentproduct results. This product is excited at the appropriate wavelengthwith incident light from a suitable source, and the fluorescenceintensity is detected by the optrode at the interface of the pyridineand alkaline phases and is measured as a function of time by means of asuitable detector system such as a spectrometer or a fluorometer. Theoptrode serves the dual function of trasmitting light from the source tothe interface where the fluorescent product is formed and oftransmitting the fluorescenct light signal from the product at theinterface to the detector system.

Providing a two phase system and a discrete interface between thepyridine phase and the alkaline phase serves to eliminate the problem ofpyridine dilution by water permeation and a continual generation of thefluorescent product at the interface is facilitated.

In accordance with another embodiment of the subject method, laser basedremote fiber spectrometry is employed for the detection and measurementof trace to macro concentrations of halogenated hydrocarbons from singleor multiple samples, from the same location or multiple locations, at asite remote from the detection system. A network of single strand fiberoptics or fiber optic cables tipped by appropriate optrodes are placedat various field locations. A laser light of the appropriate wavelengthis focused into these single strand optical fibers or cables. Theoptical fibers or cables are coupled to various samples of the analyteat various locations or from the same locus through the optrodes. Thelight, after interaction with the analyte, is collected and transmittedback through the same optical fibers or cables to a specially designeddetection system such as a spectrometer where the returning light isspectrally sorted and analyzed.

The following examples best serve to illustrate the principle of thesubject invention and describe preferred embodiments thereof and are notto be construed as limiting the invention in any manner or to anyprecise form:

EXAMPLE 1 The Construction Of The Optrode

The optical fiber was purchased from Valtec, Boylston, Massachusetts. Ithad a 245 μm glass core, a silicon clad, and a polyvinyl sheath. It hadan outer diameter of 500 μm. The end of the fiber was carefully polishedusing a 30 through 1 micron lapping film according to methods known inthe art. Approximately 1.2 cm of the clad and buffer were then removedfrom the polished end. The stripped fiber was immersed in concentratedsulfuric acid to assure that all the cladding had been removed. Theacid-cleaned fiber was then washed in distilled water and dried. A 25 μlcapillary tube was selected which loosely fitted over the sheatherportion of the fiber optic. The fiber was placed in this capillary tubeso that the tip of the stripped end was about 1.5 cm from the edge. Thecapillary was then filled with EPO-TEK 301 epoxy (Epoxy Technology,Inc., Billerica, Mass.) from the back end where the sheathed fiber waslocated, by pulling a vacuum at the other end of the capillary where thestripped fiber was located, until about 2 mm of the bare fiber wascovered. 10.75M KOH was then injected into the open end of the capillaryusing a very fine needle and a micro syringe until it was just below theend (about 1 mm). Spectral grade pyridine was then injected until itsvolume equaled that of the KOH. A membrane was glued to the end of thecapillary using Light-weld No. 415, UV light curing adhesive, obtainedfrom American Chemical and Engineering, Torrington, Conn. The membranewas made of mylar (polyethylene terephthalates, Dupont, Wilmington, Del.whose surface had been electrostatically etched. Once the adhesive wascured and the membrane was tightly bonded to the end of the capillary,the same glue was applied behind the membrane on the outside of thecapillary and a retaining sleeve was pulled over the membrane onto thecapillary and UV cured. The sleeve was stretched so that it could bepulled over the capillary. The completed optrode was then placed in aprotective shield.

FIG. 1 is a cross-sectional view of the subject optrode 40 shownimmersed in test solution 24. The first end of capillary tube 12 isattached to fiber optic 14 by some attaching means such as UV settingepoxy cement 18. A protective sheath 10 is provided for fiber optic 14.A proximate or first end of fiber optic 14 is operationally connected toan illumination source and a detector means, such as a fluorimeter orspectromater. Column 16 of an alkaline reagent is disposed adjacent tothe first end of capillary tube 12. Column 20 of pyridine or pyridinederivative is disposed next to and in contact with column 16 of thealkaline reagent preferably such that the surface of contact 32 isadjacent the distal end face 30 of fiber optic 14. This configurationensures that light from fiber optic 14 illuminates pyridine column 20where the concentration of OH⁻ and consequently of the Fujiwara productis highest. The second end 34 of capillary tube 12 is preferably cappedby a semipermeable membrane 26 glued or fixed to the capillary tube bysome attaching means such as epoxy cement 28 or by welding. Membrane 26is preferentially permeable to halogenated hydrocarbons but impermeableto pyridine and water. For volatile halohydrocarbons, membrane 26 may bereplaced by a bubble.

FIG. 2 is a detailed diagram showing the various components thereof. Thesix key components are (1) the glass-core fiber optic 14, with itsoptional cladding 18, (2) the glass capillary 44 which houses theoptrode components attached with a suitable seal 22 and reagents, (3)pyridine or pyridine-based reagent 26 which is the indicator compoundfor the halohydrocarbons, (4) alkali reagent 30 to maintain the pH ofpyridine at about 10, (5) a membrane such as a paraffin or mylar film 34to keep the pyridine 26 inside the optrode and the water outside theoptrode, while passing the halohydrocarbons, and (6) a shield 38 toprotect the optrode while in use; and an optional air space 42 includedto help further to keep water out of the optrode.

EXAMPLE 2 Nicotinamide As The Indicator Compound

These experiments for the detection of RCl.sub.(2+n) were based on thereaction of chloroform (CHCl₃) with nicotinamide. FIG. 3 showsabsorption spectra obtained for samples of nicotinamide to which varyingamounts of chloroform were added. A strong absorption peak observed at372 nm changed with CHCl₃ concentration. When these nicotinamide-CHCl₃mixtures were irradiated at this wavelength, a fluorescence emission at467 nm was observed whose intensity was CHCl₃ concentration dependent.Experiments were also run in the visible range with excitation ofnicotinamide-CHCl₃ samples at 415 nm which fluoresced at 487 nm. FIG. 4shows spectra of nicotinamide fluorescence with 5 ppm of CHCl₃ present.The measurements indicated that the nicotinamide system was essentiallypH independent and that it was very insoluble in water which areimportant in sensor applications.

EXAMPLE 3 Pyridine As The Indicator Compound

Pyridine exhibits a strong absorption peak at 372 nm and a weaker one at530 nm. The absorption at 372 changed predictably with the addition ofCHCl₃. The strength of the absorption at 530 nm was chosen formeasurement as a function of CHCl₃ concentration to determine ifabsorption levels at the weaker 530 nm peak could be utilized formeasuring low levels of chloroform. Alternatively, when employing anargon laser irradiation source, the 488 nm or the 514 nm absorptionpeaks were used to measure the levels of chloroform. FIG. 5 shows thatusing the 530 nm absorption peak, CHCl₃ concentrations of less than 1ppm could still be measured. Pyridine and KOH are purchased asanalytical reagents. Distilled water is used in the preparation of allreagents. The pyridine is used in the pure state where as KOH is madeinto a 10.75 M aqueous solution. It is critical to control KOHconcentration as it affects the water content of the system. 10.75 M KOHkeeps the water concentration at the optimum 7%. If the KOH molarity istoo low, the spectral absorbance at 535 nm increases until it reachesthe maximum and then decreases as increasing amounts of water diffuseinto the pyridine phase. If the amount of KOH is too high, a maximumabsorbance is never attained because there is an insufficient amount ofwater and KOH would be present in the pyridine phase. KOH concentrationsbetween 10 and 11 M worked the best.

The optrode and method of the subject invention are thus are suitablefor monitoring volatile organic chloride contaminants in aqueoussystems. The subject optrode is able to detect and quantifysub-part-per-million concentrations of organic chlorides in aqueoussolutions. The fiber optic system used in the subject invention enablesthe measurement of organic chloride where the sample and detectionsystem are separated by a distance of greater than 500 meters of opticalfiber. It is also possible by the use of the subject method tosimultaneously measure organic chloride content in multiple samples fromthe same location or from different locations that are not too farapart. The subject method is specific to organic compounds containingtwo or more chlorines and sensitive to 0.1 part per million, andreproducible within ±3%. The method is also free from interferences fromother constituents in the sample when the end of the capillary is cappedby a semipermeable membrane. The optrode has a useful shelf life as itis stable in aqueous systems for more than three months.

The above embodiments were chosen and described in order to explain bestthe principles and the practical applications of the subject inventionthereby to enable those skilled in the art to utilize the invention invarious other embodiments and various modifications as are suitable fortne particular use contemplated. The foregoing description of somepreferred embodiments of the invention, therefore, have been presentedonly for purposes of description and illustration of the subjectinvention. It is not intended to be exhaustive or to limit the inventionto the precise forms disclosed, and many modifications and variationsthereof would become obvious to those skilled in the art from theteachings and disclosure herein. It is intended that the scope of theinvention is best defined by the appended claims.

We claim:
 1. As an article of manufacture an optrode for chemicallysensing halogenated hydrocarbons comprising the elements:a capillarytube capped at one end by a semipermeable membrane of porous membrane; afiber optic attached at a distal end thereof to a second end of saidcapillary tube by attaching means, said fiber optic extending into saidcapillary tube, a proximal end of said fiber optic being connected to anillumination source and a detector means; a column of a first reagentcomprising pyridine or a pyridine derivative disposed in said capillarytube adjacent said capped end; and a column of a second reagentcomprising an alkali disposed in said capillary tube adjacent to and incontact with said column of said first reagent such that a surface ofcontact between said alkali and said first reagent is adjacent saiddistal end of said fiber optic.
 2. The optrode of claim 1 wherein saidfirst reagent is pyridine and said alkali is selected from the groupconsisting of potassium hydroxide, sodium hydroxide and lithiumhydroxide.
 3. The optrode of claim 2 wherein said alkali reagent isspotassium hydroxide.
 4. The optrode of claim 3 wherein said membrane isselected from a group consisting of mylar, paraffin film,electrostatically treated mylar and polycarbonate films.
 5. As anarticle of manufacture, a two-phase detection system comprising:acapillary tube capped at one end by a semipermeable membrane or porousmembrane; a sensor means attached to a second end of said capillary tubeby attaching means so as to extend into said capillary tube, a secondend of said sensor means being connected to a detector means; a columnof a first reagent comprising pyridine or a pyridine derivative disposedin said capillary tube adjacent to said capped end thereof; a column ofa second reagent comprising an alkali disposed in said capillarly tubeadjacent to and in contact with said column of said first reagent suchthat a surface of contact between said alkali and said first reagent isadjacent the second end of said sensor means; and said capped end ofsaid capillary tube being adapted to be placed in contact with asolution of an analyte containing a halogenated hydrocarbon.
 6. Thearticle of claim 5 wherein said alkali is potassium hydroxide and saidfirst reagent is pyridine.